Lewis Acids, Bases, and Complex Ions

Lewis Acids and Bases

Definitions

• Lewis Acid: Any species that can accept a pair of electrons.

• Lewis Base: Any species that can donate a pair of electrons.

• Formation of a coordinate covalent bond is central to Lewis acid-base chemistry: one atom contributes both electrons to the bond

• Lewis Acid-Base Adduct: A compound containing a newly formed coordinate covalent bond between a Lewis acid and a Lewis base.

Examples

• Fluoride (F⁻) + Boron Trifluoride (BF₃) → Adduct (F₃B-F)

  • F⁻ (donates electrons) = Lewis Base

  • BF₃ (accepts electrons) = Lewis Acid

• Silver Ion (Ag⁺) + Ammonia (NH₃) → Complex Ion [Ag(NH₃)₂]⁺

  • NH₃ (donates electrons) = Lewis Base

  • Ag⁺ (accepts electrons) = Lewis Acid

• Sulfur Trioxide (SO₃) + Oxygen (O) → Adduct (SO₄)

  • O (donates electrons) = Lewis Base

  • SO₃ (accepts electrons) = Lewis Acid

Comparison to Bronsted-Lowry

• Bronsted-Lowry Acid: Proton donor.

• Lewis Acid: Electron pair acceptor.

• Bronsted-Lowry Base: Proton acceptor.

• Lewis Base: Electron pair donor.

Connection to Solubility (Ksp)

• Complex ion formation affects the solubility of sparingly soluble salts.

• Consideration of all reactions (including complex ion formation) is crucial when determining the overall solubility and applying Le Chatelier's principle.

Complex Ions and Coordination Chemistry

• Complex ions and coordination compounds typically contain a metal center atom bonded to ions or molecules (ligands) via coordinate covalent bonds.

• Ligands: Ions or molecules attached to the metal center.

  • Act as Lewis bases that bond to the metal (Lewis acid).

• Kf (formation constant) will be discussed in the next video.